1. Field of the Invention
The present invention relates to plasma display devices.
2. Description of Related Art
In recent years, as the size of display devices has increased, there has been a demand for a thinner display device, and consequently various thin display devices have become commercially available. The AC (alternating current discharge) type plasma display panel (hereinafter simply as xe2x80x9cPDPxe2x80x9d), a thin display device, has attracted much attention.
The PDP includes a matrix of discharge cells corresponding to pixels. The discharge cell is allowed to emit light by the discharge phenomenon. There are only two states for the cell, i.e., the xe2x80x9clight emittingxe2x80x9d state in the maximum luminance and the xe2x80x9cnon-light emittingxe2x80x9d state in the minimum luminance. Gradation driving is performed based on a subfield drive method in order to allow the discharge cell to display the intermediate level luminance corresponding to an input video signal.
In the gradation driving based on the subfield drive method, one field in a display period consists of a plurality of subfields, and each subfield is allocated with a light emission number (light emitting periods) corresponding to the weight of the subfield.
FIG. 1 is a diagram showing a light emission driving format when one field in the display period is divided into four subfields, SF1 to SF4.
In FIG. 1, the subfields SF1 to SF4 are allocated the light emission numbers as follows:
SF1: 1
SF2: 2
SF3: 4
SF4: 8
Depending upon the luminance level of an input video signal, light is emitted in one or a combination of the subfields SF1 to SF4. If for example the luminance level of the input video signal is xe2x80x9c4xe2x80x9d, only the subfield SF3 among the subfields SF1 to SF4 is used for emitting light. At the time, light is emitted four times in the subfield SF3. Therefore, light emission is performed four times during the display period for one field, and the luminance corresponding to the luminance level xe2x80x9c4xe2x80x9d is observed. If the luminance level of the input video signal is xe2x80x9c13xe2x80x9d, light emission is performed in the subfields SF1, SF2 and SF4. At the time, light emission is performed once in the subfield SF1, twice in the subfield SF2, and eight times in the subfield SF4. Therefore, light emission is performed thirteen times altogether during the display period for one field, and the luminance corresponding to the luminance level xe2x80x9c13xe2x80x9d is observed.
In this case, in order to increase the luminance of the entire screen, the number of light emission (light emitting periods) allocated to each subfield may be increased. However, the display period for one field is limited, and therefore such a method will not improve the luminance as desired.
It is an object of the present invention to provide a plasma display device capable of high luminance display by gradation driving according to the subfield drive method.
A plasma display device, according to the present invention, performs gradation driving to a plasma display panel based on a video signal. The plasma display panel has discharge cells formed at the intersections of a plurality of row electrodes corresponding to display lines and a plurality of column electrodes arranged so that they intersect the row electrodes. The plasma display device includes a driving portion and a non-selected line detection portion. The driving portion performs pixel data writing scanning for scanning each of the discharge cells on each display line according to pixel data corresponding to the video signal, and causes selective discharge. As a result this sets each of the discharge cells to one of a light emitting state and a non-light emitting state in each of a plurality of subfields constituting a display period for one field in the video signal. The driving portion also performs light emission sustaining driving for causing sustaining discharge. As a result this allows only the discharge cells in the light emitting state to emit light as many times as the number of light emissions allocated corresponding to the weight of each subfield. The non-selected line detection portion detects a non-selected line to be a display line on which all the discharge cells are not subjected to the selective discharge based on the pixel data. The driving portion performs the pixel data writing scanning only to each of the display lines excluding the non-selected line.